linux-kernel - Re: [PATCH] ASoC: fsl_ssi: Override bit clock rate based on slot number

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Date:   Sat, 25 Nov 2017 23:29:48 +0100
From:   Lukasz Majewski <lukma@...x.de>
To:     Nicolin Chen <nicoleotsuka@...il.com>
Cc:     Arnaud Mouiche <arnaud.mouiche@...oxia.com>, broonie@...nel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        alsa-devel@...a-project.org, tiwai@...e.com, perex@...ex.cz,
        lgirdwood@...il.com, fabio.estevam@....com, timur@...i.org,
        caleb@...me.org, max.krummenacher@...adex.com, mpa@...gutronix.de,
        mail@...iej.szmigiero.name
Subject: Re: [PATCH] ASoC: fsl_ssi: Override bit clock rate based on slot
 number

Hi Nicolin,

> On Wed, Sep 13, 2017 at 10:02:20AM +0200, Arnaud Mouiche wrote:
> 
> > >Could you please give me a few set of examples of how you set
> > >set_sysclk(), set_tdm_slot() with the current driver? The idea
> > >here is to figure out a way to calculate the bclk in hw_params
> > >without getting set_sysclk() involved any more.  
> 
> > Here is one, where a bclk = 4*16*fs is expected  
> 
> > In another setup, there are 8 x 16 bits slots, whatever the number
> > of active channels is.
> > In this case bclk = 128 * fs
> > The number of slots is completely arbitrary. Some slots can even be
> > reserved for communication between codecs that don't communicate
> > with linux.  
> 
> In summary, bclk = sample rate * slots * slot_width;
> 
> I will update my patch soon.
> 
> > >Unfortunately, it looks like a work around to me. I understand
> > >the idea of leaving set_sysclk() out there to override the bit
> > >clock is convenient, but it is not a standard ALSA design and
> > >may eventually introduce new problems like today.  
> > 
> > I agree. I'm not conservative at all concerning this question.
> > I don't see a way to remove set_sysclk without breaking current TDM
> > users anyway, at least for those who don't have their code
> > upstreamed.  
> 
> Which TDM case would be broken by this removal? The only impact
> that I can see is that the ASoC core returns an ENOTSUPP for a
> set_sysclk() call now, which is something that a dai-link driver
> should have taken care of anyway.
> 
> > All information provided through snd_soc_dai_set_tdm_slot( cpu_dai,
> > mask, mask, slots, width ) should be enough
> > In this case, for TDM users
> > 
> >    bclk = slots * width * fs   (where slots is != channels)  
> 
> > will manage 99 % of the cases.
> > And the remaining 1% will concern people who need to hack the kernel
> > so widely they don't care about the set_sysclk removal.  
> 
> A patch from those people will be always welcome.
> 
> > - fsl-asoc-card.c : *something will break since
> > snd_soc_dai_set_sysclk returned code is checked*  
> 
> I've already submitted a patch to ignore all ENOTSUPP.

Nicolin, do you know what happened with this patch? I couldn't find it
in current linux/master.

Has it been applied to any asoc tree for being upstreamed?

Best regards,

Lukasz Majewski

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